Synchrotron X-ray Computed Tomography Research Articles

Visualization of stepwise electrode decomposition in a nail penetrated commercial lithium-ion cell using low-temperature synchrotron X-ray computed tomography

The transition towards zero carbon emissions in power generation hinges on the integration of efficient electrical energy storage systems, with lithium-ion batteries (LIBs) positioned as a pivotal technology. While generally safe, deviations in their operational guidelines due to manufacturing defects or misuse can lead to critical safety concerns, notably thermal runaway (TR) events. Internal short circuits (ISCs) are primary initiators of TR within LIBs. For abuse testing, ISCs are often triggered by nail penetration. This study explores the morphological changes and mechanisms underlying ISC-induced TR in LIBs using operando synchrotron X-ray computed tomography (SXCT) at subzero temperatures. A novel cryogenic setup was developed to control a stepwise temperature increase in the damaged sample while monitoring electrochemical characteristics and simultaneously enabling acquisition of high-resolution SXCT images. The findings reveal that conducting nail penetration at minus 80 °C prevents immediate TR, enabling detailed analysis of subsequent structural and electrochemical behavior during controlled thawing. Thus, the initiation of TR processes at localized ISC sites has been observed, evidenced by voltage fluctuations and morphological changes, such as cathode material cracking and decomposition. These results underscore the importance of temperature control in mitigating TR risks and provide critical insights into the internal dynamics of LIBs under abusive conditions. The developed cryogenic SXCT methodology offers a powerful tool for non-destructive, high-resolution investigation of battery failure mechanisms, contributing to the enhancement of LIB safety.

The impact of coaxial gas technology on the morphology of powder by gas atomisation and the additive manufactured mechanical performance

ABSTRACT Metal powders are essential for additive manufacturing (AM), with their morphology significantly impacting the performance of AM components. Gas atomisation (GA) is a common method for producing metal powders due to its efficiency and cost-effectiveness. However, GAed powders often exhibit defects such as alien powders, satellite powders, and hollow powders, which can adversely affect the AM process. To address these challenges, coaxial gas technology has been introduced and analysed through numerical simulation. Our study involved comparing GA processes with and without coaxial gas technology to generate two types of powders. These powders were assessed using Synchrotron X-ray computed tomography (SXCT) and classification algorithms. The pores in AM components manufactured from these powders were examined using SXCT, and their mechanical properties were evaluated through tensile tests. The findings of our research validate the effectiveness of coaxial gas technology in reducing powder defects and enhancing the performance of AM components.

Ex-situ characterization and simulation of density fluctuations evolution during sintering of binder jetted 316L

Efficient density evolution during sintering of the as-printed component is vital to reach full densification and required properties of binder jet (BJT) components. However, due to the high porosity and brittle nature of the green compact, analysis of the microstructure development during sintering is very difficult, resulting in lack of understanding of the densification process. Density development from green state (57 ± 1.6 %) up to full density (99 ± 0.3 %) was characterized by high-resolution synchrotron X-Ray computed tomography (SXCT) on BJT 316L samples from ex-situ interrupted sintering tests. Periodicity of density fluctuations along the building direction was revealed for the first time and was related to the layer thickness of ∼ 42 µm during printing that decreased down to ∼ 33 µm during sintering. Sintering simulations, utilizing a continuum sintering model developed for BJT, allowed to replicate the density evolution during sintering with a mean error of 2 % and its fluctuation evolution from green (1.66 %) to sintered (0.56 %) state. Additionally, simulation of extreme particle size segregation (1 µm to 130 µm) suggested that non-optimized printing could lead to undesirable density fluctuation amplitude rapid increase (∼10 %) during sintering. This might trigger the nucleation of defects (e.g., layer delamination, cracking, or excessive residual porosity) during the sintering process.

Mechanical behaviour and microstructure of methane hydrate-bearing sandy sediment observed at various spatial scales

Methane hydrates (MHs) are considered an alternative energy resource but also a potential source of geo-hazards and climate change. The physical/mechanical properties of gas hydrate-bearing sandy sediments are strongly dependent on the distribution of hydrates within the pore space. The purpose of this study is to investigate morphologies and pore-habits of MHs formed in sandy sediments by means of experiments that probe a wide range of scales, from the pore scale – using Synchrotron X-Ray Computed Tomography (SXRCT) and optical microscopy – to the core scale, through mechanical property measurements. The same synthetic sands are used, in which MHs are generated successively under excess gas and excess water conditions. At the macroscopic (core) scale, MH pore habits are inferred by comparing the measured sonic wave velocities to velocities calculated from rock physics models and further assessed via triaxial compression tests. Furthermore, Magnetic Resonance Imaging is used to investigate the kinetics of MH formation and distribution along the core height. The pore habits and MH morphologies are directly visualized at the pore (grain) scale by SXRCT and, with still better spatial and temporal resolution, by transmission optical microscopy, revealing some more complex morphologies than in the hydrate pore habits commonly admitted.

Investigating the Influence of Inlet Relative Humidity on Polymer Electrolyte Membrane Fuel Cell Performance by Visualizing 4-D Water Distributions in Gas Diffusion Layers

The catastrophic effects of atmospheric greenhouse gases and the depletion of non-renewable resources has led to the urgency to develop clean, sustainable energy technologies to meet increasing energy demands. However, the intermittent nature of current renewable energy technologies warrants the acquisition of on-demand renewable energy through either energy production or storage methods. Polymer electrolyte membrane fuel cells (PEMFCs) are promising candidates for this task, as they utilize the most abundant element on Earth, hydrogen, to produce high amounts of power under rapid changes in load with little to no greenhouse gas emissions (1). Therefore, PEMFCs have great potential to help offset the negative impact of atmospheric pollution due to excessive carbon emissions. However, liquid water management issues associated with high power output of the fuel cell typically leads to reduced performance and durability of the fuel cell, and thereby hinders global implementation of these devices (2). To minimize these losses and improve GDL material designs, an understanding of the relationship between product liquid water distributions in the cathode GDL and transport properties of PEMFCs under varying operating conditions is highly valuable. Previous works have characterized the effect of operating temperature on liquid water pathways and distributions in GDLs by visualizing operando PEMFCs with 3D imaging techniques such as X-ray computed tomography (CT) (3). The high-speed, high-resolution capabilities of these imaging techniques enable the visualization of dynamic pore-scale activity to elucidate transport mechanisms in the GDL.In this work, the effect of inlet relative humidity on the formation and distribution of liquid water pathways in cathode GDLs is investigated by imaging a PEMFC operando with synchrotron X-ray CT at high spatial resolution, enabling the resolution of water in the individual pores of the GDL. The contribution of a microporous layer (MPL) is also explored by imaging a cell with an MPL and without. Imaging is conducted on a specialized cell designed to facilitate continuous rotation about the CT stage, enabling fast acquisition of consecutive scans to achieve high temporal resolution useful for visualizing the dynamic development of preferential water pathways. Additionally, electrochemical impedance spectroscopy was performed to quantify mass transport losses. The sequence of CT images was utilized to capture the dynamics of liquid water development as well as stabilized water distributions. Visualizing the reconstructed images shows that as current increases, water production increases, and the development of water pathways to breakthrough at the flow field interface is observed. Additionally, results show that an increase in relative humidity led to a significant increase in cathode GDL water saturation.The contribution of this study to understanding transport mechanisms in GDL materials is significant to the characterization and optimal design of materials for improved PEMFC performance. Ultimately, the goal of this work is to accelerate the worldwide adoption of PEMFCs as a sustainable, reliable solution to replace conventional carbon-emitting energy sources.1. Alaswad et al., J. Hydrog. Energy, 41, (2016)2. Nagai et al., J. Power Sources, 435, (2019)3. D. Shum et al., Electrochem. Acta, 256, (2017)

Quantification of the Deep Discharge Induced Asymmetric Copper Deposition in Lithium‐Ion Cells by Operando Synchrotron X‐Ray Tomography

Lithium‐ion cells connected in series are prone to an electrical safety risk called overdischarge. This paper presents a comprehensive investigation of the overdischarge phenomenon in lithium‐ion cells using operando nondestructive imaging. The study focuses on understanding the behavior of copper dissolution and deposition during overdischarge, which can lead to irreversible capacity loss and internal short‐circuits. By utilizing synchrotron X‐ray computed tomography (SXCT), the concentration of dissolved and deposited copper per surface area is quantified as a function of depth of discharge, confirming previous findings. The results also highlight for the first time a nonuniform distribution pattern for copper deposition on the cathode. This research provides insights for safer battery cell design.

Tailoring the enhanced mechanical behavior of 6061Al composites via nano SiCp and micron B4Cp addition

In this work, the hybrid micron B4C particles (m-B4Cp) and nano SiC particles (n-SiCp) reinforced 6061Al matrix composites were prepared by powder metallurgy. The synergistic effects of hybrid m-B4Cp and n-SiCp were investigated. The results showed that m-B4Cp were well dispersed in the matrix, while n-SiCp were uniformly distributed inside the grains as well as at the grain boundaries. The coupled addition of n-SiCp and m-B4Cp significantly refined the grain size of matrix from 3.60 μm to 0.91 μm. The synchrotron X-ray computed tomography (SR-CT) revealed that the volume of pores increased with increase of particle content. Compared with the composites reinforced with only one type of particle, the 6061Al composites reinforced with micro and nano dual-size particles possessed higher tensile strength, while maintaining reasonable plasticity. The strengthening contributions to the yield strength improvement of 6010Al matrix composites reinforced with micro and nano dual-size particles are resulted from thermal expansion mismatch strengthening, fine grain strengthening and Orowan strengthening caused by n-SiCp.

Synchrotron X-ray computed tomography analysis of the morphological characterization of aluminum alloy powders produced by gas atomization

Gas atomization (GA) is a highly efficient and cost-effective method of producing metal powder for additive manufacturing. However, powders with defects can significantly reduce the performance of manufactured components. Therefore, accurately characterizing powder morphology is crucial to evaluating powder quality. This study uses synchrotron X-ray computed tomography (SXCT) to measure the characteristics of aluminum alloy powders. Morphological parameters such as mean Feret diameter, aspect ratio, sphericity, etc., are obtained from reconstructed 3D images. Statistical analysis shows that as particle size increases from <38.5 μm to >100 μm, the proportion of satellite and hollow powders increases from 25.97% to 59.29% and from 3.60% to 13.60%, respectively, while the proportion of irregular powder only slightly decreases about 3%. Additionally, the irregularity of the powder increases with increasing diameter. Overall, this study highlights the importance of characterizing powder morphology and demonstrates the potential of SXCT for such analysis.

Multi-level X-ray computed tomography (XCT) investigations of commercial lithium-ion batteries from cell to particle level

Adopting X-ray computed tomography (XCT) for ex-situ characterization of battery materials has gained interest in the past decade. The main goal of this paper is to demonstrate the effectiveness of several X-ray computer tomography techniques to study commercial batteries. General guidelines are provided to select the most suitable imaging equipment and parameters for investigations of lithium-ion batteries, spanning the length scales from cell to electrode, down to particle level. Relevantly, such parameters would also be suitable for operando experiments. Safety mechanisms and manufacturing inconsistencies at cell level as well as defects and inhomogeneity in cathode and anode is illustrated and quantified. Furthermore, relation of beam energy and sample-detector-distance on contrast retrieved from attenuation and phase shift is inspected using Synchrotron XCT.

A Review of X‐Ray Imaging at the BAMline (BESSY II)

The hard X‐ray beamline BAMline at BESSY II (Berlin, Germany) has now been in service for 20 years. Several improvements have been implemented in this time, and this review provides an overview of the imaging methods available at the BAMline. Besides classic full‐field synchrotron X‐ray computed tomography (SXCT), also absorption edge CT, synchrotron X‐ray refraction radiography (SXRR), and synchrotron X‐ray refraction tomography (SXRCT) are used for imaging. Moreover, virtually any of those techniques are currently coupled in situ or operando with ancillary equipment such as load rigs, furnaces, or potentiostats. Each of the available techniques is explained and both the current and the potential usage are described with corresponding examples. The potential use is manifold, the examples cover organic materials, composite materials, energy‐related materials, biological samples, and materials related to additive manufacturing. The article includes published examples as well as some unpublished applications.

Codependent failure mechanisms between cathode and anode in solid state lithium metal batteries: mediated by uneven ion flux

An in-depth understanding of the degradation mechanisms is a prerequisite for developing the next-generation all solid-state lithium metal battery (ASSLMB) technology. Herein, synchrotron X-ray computed tomography (SXCT) together with other probing tools and simulation method were employed to rediscover the decaying mechanisms of LiNi0.8Co0.1Mn0.1O2 (NCM)|Li6PS5Cl (LPSCl)|Li ASSLMB. It reveals that the detachment and isolation of NCM particles cause the current focusing on the remaining active regions of cathode. The extent of Li stripping and the likelihood of Li+ plating into LPSCl facing the active NCM particles becomes higher. Besides, the homogeneity of Li stripping/plating is improved by homogenizing the electrochemical reactions at the cathode side by LiZr2(PO4)3 (LZP) coating. These results suggest a codependent failure mechanism between cathode and anode that is mediated by uneven Li ion flux. This work contributes to a holistic understanding of the degradation mechanisms in ASSLMBs and opens new opportunities for their further optimization and development.

3D synchrotron imaging of muscle tissues at different atrophic stages in stroke and spinal cord injury: a proof-of-concept study

Synchrotron X-ray computed tomography (SXCT) allows 3D imaging of tissue with a very large field of view and an excellent micron resolution and enables the investigation of muscle fiber atrophy in 3D. The study aimed to explore the 3D micro-architecture of healthy skeletal muscle fibers and muscle fibers at different stages of atrophy (stroke sample = muscle atrophy; spinal cord injury (SCI) sample = severe muscle atrophy). Three muscle samples: a healthy control sample; a stroke sample (atrophic sample), and an SCI sample (severe atrophic sample) were imaged using SXCT, and muscle fiber populations were segmented and quantified for microarchitecture and morphology differences. The volume fraction of muscle fibers was 74.7%, 70.2%, and 35.3% in the healthy, stroke (atrophic), and SCI (severe atrophic) muscle fiber population samples respectively. In the SCI (severe atrophic sample), 3D image analysis revealed fiber splitting and fiber swelling. In the stroke sample (atrophic sample) muscle fiber buckling was observed but was only visible in the 3D analysis. 3D muscle fiber population analysis revealed new insights into the different stages of muscle fiber atrophy not to be observed nor quantified with a 2D histological analysis including fiber buckling, loss of fibers and fiber splitting.

Investigating the Influence of Humidity on Liquid Water Transport Mechanisms in Fuel Cell Gas Diffusion Layers Using Operando X-Ray Computed Tomography

The intermittent nature of many renewable energy sources, such as solar and wind, presents the need to acquire on-demand renewable energy either through energy storage or energy production methods. The polymer electrolyte membrane (PEM) fuel cell is quickly becoming an attractive solution as it can produce high power densities under a rapid change in load while producing zero local carbon emissions [1] and is ideal for large-scale applications, such as automotive [2]. However, barriers to their widespread implementation are attributed to the high costs associated with mass transport losses at high current density operation due to inefficiencies in liquid water management in the gas diffusion layer (GDL) [3][4]. Understanding the relationship between liquid water distributions in the cathode GDL and transport properties of PEM fuel cells under varying operating conditions can lead to improved GDL configurations for improved performance. Previously, studies have been conducted to characterize the effect of operating temperature on liquid water pathways in GDLs by using 3D imaging techniques on operando PEM fuel cells [5]. High-speed, high-resolution 3D imaging techniques, such as computed tomography (CT), enable the visualization of dynamic pore-scale effects and are advantageous in elucidating transport mechanisms in the GDL.In this work, the effect of operating relative humidity on the formation of liquid water pathways in the GDL will be explored by imaging an operando PEM fuel cell with synchrotron X-ray CT. To date, a custom PEM fuel cell has been developed in-house which features a novel design with two rotary unions on either side of the cell. The rotary unions enable continuous rotation of the cell during imaging, and thus are central to achieving high temporal resolution for visualizing the development of preferential water pathways. High spatial resolution (pixel resolution of 1.44 microns per pixel [6]) is also obtained with the synchrotron beam, which allows for the visualization of liquid water in individual pores at the microscale in the GDL. Visualizing water in the micropores of the GDL can help us further understand water transport mechanisms within the complex structure of the GDL to ultimately develop methods to expel excess water efficiently. In the next steps of this research, we will use the results from electrochemical testing and the reconstructed images of the fuel cell to draw important conclusions about the relationship between liquid water distributions in the GDL and fuel cell performance. As well, the effect that operating relative humidity has on this relationship will be determined. The aim of this work is to inform optimal design for GDL materials for improved PEM fuel cell performance, which will ultimately accelerate their utilization on a global scale as a reliable and sustainable energy source.[1] P. Shrestha, CH. Lee, K. F. Fahy, M. Balakrishnan, N. Ge, and A. Bazylak, “Formation of Liquid Water Pathways in PEM Fuel Cells: A 3-D Pore-Scale Perspective,” Journal of The Electrochemical Society, vol. 167, no. 5, p. 054516, Jan. 2020, doi: 10.1149/1945-7111/ab7a0b.[2] S. Park, J. W. Lee, and B. N. Popov, “A review of gas diffusion layer in PEM fuel cells: Materials and designs,” International Journal of Hydrogen Energy, vol. 37, no. 7, pp. 5850– 5865, Apr. 2012, doi: 10.1016/J.IJHYDENE.2011.12.148.[3] Y. Nagai et al., “Improving water management in fuel cells through microporous layer modifications: Fast operando tomographic imaging of liquid water,” Journal of Power Sources, vol. 435, p. 226809, Sep. 2019, doi: 10.1016/J.JPOWSOUR.2019.226809.[4] U. U. Ince et al., “3D classification of polymer electrolyte membrane fuel cell materials from in situ X-ray tomographic datasets,” International Journal of Hydrogen Energy, vol. 45, no. 21, pp. 12161–12169, Apr. 2020, doi: 10.1016/J.IJHYDENE.2020.02.136.[5] Hong Xu, Shinya Nagashima, Hai P. Nguyen, Keisuke Kishita, Federica Marone, Felix N. Büchi, Jens Eller, Temperature dependent water transport mechanism in gas diffusion layers revealed by subsecond operando X-ray tomographic microscopy, Journal of Power Sources, Volume 490, 2021, 229492, ISSN 0378-7753, https://doi.org/10.1016/j.jpowsour.2021.229492.[6] Canadian Light Source, “Detectors,” BMIT. [Online]. Available: https://bmit.lightsource.ca/tech-info/detectors/. [Accessed: 05-Apr-2022].

4D imaging of void nucleation, growth, and coalescence from large and small inclusions in steel under tensile deformation

• High spatial and temporal resolution synchrotron X-ray CT enabled 4D imaging of void nucleation, growth, and coalescence with unprecedented details. • Large inclusion particles in SA508 steel led to large and prolate voids which, while striking, did not affect crack formation. • The final fracture was induced by densely populated carbide precipitates that led to small but closely spaced voids which quickly coalesced to form micro-cracks. • The results challenge established theories on ductile fracture and could potentially lead to new strategies for steel making. Samples of SA508 grade 3 nuclear pressure vessel ferritic steel were subjected to tensile straining whilst being simultaneously imaged in 3D in real time using high resolution, high frame rate time-lapse synchrotron computed tomography (CT). This enabled direct observation of void development from nucleation, through growth to coalescence and final failure validating many inferences made post-mortem or by theoretical models, as well as raising new points. The sparse, large inclusions were found to nucleate voids at essentially zero plastic strain (consistent with zero interfacial strength); these became increasingly elongated with straining. In contrast, a high density of small spherical voids were found to nucleate from the sub-micron cementite particles at larger strains (> 200%) only in the centre of the necked (high triaxiality) region. An interfacial strength approaching 2100 MPa was inferred and soon after their nucleation, these small voids coalesce to form internal microcracks that lead to the final failure of the specimen. Perhaps surprisingly, under these conditions of generally low triaxial constraint the large voids are simply cut across and appear to play no significant role in determining the final failure. The implications of these results are discussed in terms of ductile fracture behaviour and the Gurson model for ductile fracture.

High‐Performance 3D Li‐B‐C‐Al Alloy Anode and its Twofold Li Electrostripping and Plating Mechanism Revealed by Synchrotron X‐Ray Tomography

The uncontrollable Li electrostripping and plating process that results in dendritic Li growth and huge volume change of Li anode limits the practicality of Li metal batteries (LMBs). To simultaneously address these issues, designing three‐dimensional (3D), lithiophilic and mechanically robust electrodes seems to be one of the cost‐effective strategies. Herein, a new 3D Li‐B‐C‐Al alloy anode is designed and fabricated. The prepared 3D alloy anode exhibits not only superior lithiophilicity that facilitates uniform Li nucleation and growth but also sufficient mechanical stability that maintains its structural integrity. Superior performance of the prepared 3D alloy is demonstrated through comprehensive electrochemical tests. In addition, non‐destructive and 3D synchrotron X‐ray computed tomography (SX‐CT) technique is employed to investigate the underlying working mechanisms of the prepared alloy anode. A unique twofold Li electrostripping and plating mechanism under different electrochemical cycling conditions is revealed. Lastly, improved performance of the full cells built with the 3D alloy anode and LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode corroborate its potential application capability. Overall, the current work not only showcases the superiority of the 3D alloy as potential anode material for LMBs but also provides fundamental insights into its underlying working mechanisms that may further propel its research and development.

On Acquisition Parameters and Processing Techniques for Interparticle Contact Detection in Granular Packings Using Synchrotron Computed Tomography.

X-ray computed tomography (XCT) is regularly employed in geomechanics to non-destructively measure the solid and pore fractions of soil and rock from reconstructed 3D images. With the increasing availability of high-resolution XCT imaging systems, researchers now seek to measure microfabric parameters such as the number and area of interparticle contacts, which can then be used to inform soil behaviour modelling techniques. However, recent research has evidenced that conventional image processing methods consistently overestimate the number and area of interparticle contacts, mainly due to acquisition-driven image artefacts. The present study seeks to address this issue by systematically assessing the role of XCT acquisition parameters in the accurate detection of interparticle contacts. To this end, synchrotron XCT has been applied to a hexagonal close-packed arrangement of glass pellets with and without a prescribed separation between lattice layers. Different values for the number of projections, exposure time, and rotation range have been evaluated. Conventional global grey value thresholding and novel U-Net segmentation methods have been assessed, followed by local refinements at the presumptive contacts, as per recently proposed contact detection routines. The effect of the different acquisition set-ups and segmentation techniques on contact detection performance is presented and discussed, and optimised workflows are proposed.

New X-Ray Microtomography Setups and Optimal Scan Conditions to Investigate Methane Hydrate-Bearing Sand Microstructure

Abstract Methane hydrates, which are naturally formed at high pressures and low temperatures in marine and permafrost sediments, represent a great potential energy resource but also a considerable geo-hazard and climate change source. Investigating the grain-scale morphology of methane hydrate-bearing sandy sediments is crucial for the interpretation of geophysical data and reservoir-scale simulations in the scope of methane gas production as methane hydrate morphologies and distribution within the porous space significantly impact their macroscopic physical/mechanical properties. X-ray computed tomography (XRCT) and synchrotron X-ray computed tomography (SXRCT) are commonly used to analyze the microstructure of geo-materials. However, methane hydrates exist only at high pressures (up to several megapascals) and low temperatures (a few degrees Celsius). This article describes the development of three experimental setups, which aim at creating methane hydrates in sandy sediment, adapted to XRCT and SXRCT observations. The advantages and drawbacks of each setup are discussed. The discussions focus on the effects of the choice of the system to control temperature and pressure on the quality of images. The obtained results would be useful for future works involving temperature control systems or pressure control systems, or both, adapted to XRCT and SXRCT observations of various geo-materials.

Laboratory-based x-ray computed tomography for 3D imaging of samples in a diamond anvil cell in situ at high pressures.

Three-dimensional (3D) visualization of a material under pressure can provide a great deal of information about its physical and chemical properties. We developed a technique combining in-house x-ray computed tomography (XCT) and a diamond anvil cell to observe the 3D geometry of a sample in situ at high pressure with a spatial resolution of about 610 nm. We realized observations of the 3D morphology and its evolution in minerals up to a pressure of 55.6 GPa, which is comparable to the pressure conditions reported in a previous synchrotron XCT study. The new technique developed here can be applied to a variety of materials under high pressures and has the potential to provide new insights for high-pressure science and technology.

An experimental investigation on methane hydrate morphologies and pore habits in sandy sediment using synchrotron X-ray computed tomography

As pore-scale morphologies and spatial distribution (pore habits) of natural gas hydrates in marine sediments considerably affect their physical/mechanical properties, they have extensively been investigated by X-ray computed tomography (XRCT) and especially synchrotron X-Ray computed tomography (SXRCT). While both image spatial and scan temporal resolutions are being improved over time, it is still challenging to distinguish water from methane hydrate in an image due to their low absorption contrast. In this study, methane hydrate formation and growth in wet sand were observed at submicron/micron scale using SXRCT. Saline water (Potassium iodide - KI) was used in order to improve the image contrast. Evolutions of methane hydrate morphologies and distribution at both the pore and sample scales were observed. Results are discussed based on various mechanisms related to material behaviors and experimental conditions, e.g. suction variation during methane hydrate formation, local temperature gradient in the sample, and particularly the interaction of X-rays with the sample. Methane hydrate formation is interpreted as a dynamic process, favoring the Ostwald ripening. Furthermore, morphologies and pore habits of methane hydrates under excess-gas and excess-water conditions are discussed. Some recommendations are finally given for further studies on methane hydrates-bearing sediments via XRCT or SXRCT.

S-XCT experimental determination of local contact angle and meniscus shape in liquid moulding of composites

In-situ spontaneous wicking experiments were scanned using Synchrotron X-ray Computed Tomography (S-XCT) to study the meniscus shape at the fibre scale. To this end, a single tow of E-glass fibres was impregnated with a commercial epoxy resin by using a wicking fixture specially designed for such purpose. The high resolution of the S-XCT images recorded (0.325μm/pixel) allowed the direct access to the surface of the individual menisci formed between fibres and permitted a direct quantification of the contact angle as well as the local curvature measurement. The contact angle values measured were in good agreement with values reported in the literature. The experimental methodology employed was also compared with numerical results obtained using a surface minimization approach. The results obtained with the simulation tool, in terms of effective capillary pressure and meniscus shape, were in good agreement with the experimental data reported.